The detection of occult blood in body fluids and body excreta provides valuable assistance to physicians in the diagnosis of a number of abnormal physical conditions. Blood may be found in the gastric contents and in vomitus in conditions which are associated with erosion of gastric and intestinal mucous membranes, in ulcers and in carcinomas. The regular and frequent occurrence of occult blood in feces is suggestive of colon-rectal cancer, gastric or duodenal ulcers or hemorrhoids. In many of these conditions, the hemorrhage may be so slight that it is not possible to detect blood by microscopic identification, even by a skilled technician.
What has long been sought is a simple diagnostic test, rapidly and easily performed, which can be unequivocally interpreted by one with limited technical skills. Numerous tests and test devices have been and are available to the medical practitioner for detecting occult blood. However, almost all of these tests suffer from one or more shortcomings, such as an overly complex procedure, too lengthy a procedure or time required for obtaining results, or difficulties in interpreting results due to the level of skill required, false positives, or generally equivocal results.
A commonly employed test currently used to detect occult blood employs a test device in which a paper strip impregnated with a water soluble indicator system is dabbed with a sample of the specimen being tested. A positive test is indicated by a color change in the indicator test strip. Although such a device and method permit rapid performance of the test, results are sometimes difficult to interpret. This is attributable at least in part to the nature of the materials employed in the test strip and sample. That is, the use of a water soluble indicator composition in a paper test strip for detecting blood in an aqueous-based medium renders interpretation of test results difficult since the water soluble color indicator composition tends to migrate or diffuse through the paper matrix.
Similar test devices employ paper test strips impregnated with color indicator compositions which are at least in part water insoluble, thereby avoiding diffusion of the "test spot" . However, these strips require the user to have and to apply a separate reagent at the time the test is performed in order to develop the color.